The present invention relates to slicing machines for use in slicing materials such as silicon wafers for semiconductors, and more particularly to the improvement of a slicing cutter blade of the internal edge type for such slicing machines in which the cutter blade comprises an annular sheet steel body and a cutting edge formed at the inner circumferential edge of the annular sheet steel body, and which is adapted to be secured to holder means at the outer circumferential portion of the annular sheet steel body.
Heretofore, slicing cutter blades of the internal edge type used in slicing materials such as semiconductor silicon wafers have generally been tensioned by imparting uniform tension radially to the entire curcumference of the cutter blade. This process for tensioning the slicing cutter blade, however, has not provided the desired results. More particularly, the known slicing cutter blade comprises an annular sheet steel body usually made of a rolled sheet material of SUS 304 and fabricated by blanking the material with press working to form its inner and outer circumferential edges and fixing bolts holes. The rolled sheet material has elongation percentages which are different depending on the direction in which the rolling is done. Therefore, the cutting edge formed at the inner circumferential edge of the slicing cutter blade cannot retain in a truly circular shape upon tensioning. Thus, owing to the difference in the modulus of longitudinal elasticity due to the rolling direction of the material, the slicing cutter blade is tensioned with the inner circumferential edge and thus the cutting edge is deformed into an elliptical shape having a major dimension corresponding to an elongation percentage which is higher in a direction perpendicular to the rolling direction of the material. Because of this tendency, it has hitherto been essential, in a bolt tensioning process, for example, to effect adjustments in such a manner that the slicing cutter blade is tensioned strongly in the rolling direction of the material and weakly in a direction perpendicular to the rolling direction of the material. This adjustment has required much skilled labor and a prolonged time, thereby causing a bottleneck to the operation in the field. Meanwhile, in a hydraulic pressure tensioning process, the tensioning operation is quite simple and tensioning can be achieved in a relatively short period of time. However, this process has not permitted such adjustment as would obtain true circularity in a cutting edge on the inner circumferential edge of the slicing cutter blade. When the cutting edge at the inner circumferential edge of the slicing cutter blade is deformed into an elliptical shape upon tensioning, the service life of the slicing cutter blade is very short because the cutting edge becomes unbalanced when slicing is carried out.
On the other hand, a proposal has been made by the applicant of the present invention to provide, as disclosed in Japanese Patent Application Laid-Open No. 31684/79, particularly at FIG. 3 thereof, a slicing cutter blade of the internal edge type comprising an annular sheet steel body and a cutting edge formed at the inner circumferential edge of the annular sheet steel body, the slicing cutter blade being adapted to be secured at the outer circumferential portion of the annular sheet steel body to holder means such that the annular sheet steel body is forced to make contact at its tension generating section with a protuberance of a tension ring of the holder means, in which the annular sheet steel body is formed with a plurality of circumferentially arranged and equidistantly spaced circular apertures disposed substantially in a middle portion between the tension generating section and the cutting edge for generating increased circumferential stress in the cutting edge.
In the aforesaid construction, it becomes possible to generate for the same tensioning force an increased circumferential stress in the cutting edge at the inner circumferential edge when the slicing cutter blade is tensioned, the circumferential stress of the cutting edge having great importance with respect to the sharpness of the cutting edge. Thus a satisfactory circumferential stress in the cutting edge can be obtained with a relatively small tensioning force, and in fact such an advantage has been ascertained by experiments and numerical analysis.
However, the construction disclosed in Japanese Patent Application Laid-Open No. 31684/79 has still not eliminated the difference in elongation percentage due to the rolling direction of the material.